1. Field of the Invention
The present invention relates to a maskless exposure method, which is used in a manufacturing process for an LCD panel or the like, for instance.
2. Description of the Related Art
A size of a glass substrate (hereinafter referred to as a substrate) used for manufacturing LCD panels, for example, has been increased because of an increase in size of the panel or to improve the production efficiency. In addition, a requirement of display resolution with respect to the large substrate is apt to increase rather than maintaining the same level.
As the size of the substrate increases, a mask for exposure is also increased in size. Then, how to reduce cost of the mask has become one of problems in the mass production. Therefore, a maskless exposure system has been tried, in which ON and OFF of light to be projected is controlled without using a mask so that a pattern is directly burned on the substrate on which a resist is applied.
In this maskless exposure system, a drawing head that emits light controlled by an optical modulator scans the substrate held on a stage so that a pattern is drawn. On this occasion, the stage holding the substrate is required to move with high precision without speed variation. If the maskless exposure system cannot constantly maintain a position and an angle of the head, speed variation, rectilinearity and positioning accuracy of the stage, a drawing start timing, and a drawing magnification (magnitude of width) of exposing light with high accuracy, quality of the product may be deteriorated. In addition, as an essential function of an exposure machine, it is required to have a high accuracy of alignment in the exposure process with accurate positioning with respect to a base pattern.
Here, with reference to FIGS. 16 and 17, a conventional method of calibrating the maskless exposure machine is described. In the conventional method, a jig illustrated in FIG. 16 is used for calibrating a state of drawing position accuracy of a maskless exposure apparatus, or the calibration is performed in accordance with a positional deviation of an exposure pattern with respect to a reference mark as illustrated in FIG. 17. Note that the method illustrated in FIG. 16 is disclosed in Japanese Patent Application Laid-open No. 2005-43576, and the method illustrated in FIG. 17 is disclosed in Japanese Patent Application Laid-open No. 2005-283893.
The jig illustrated in FIG. 16 includes a calibrating plate 110 to be disposed on the stage of the exposure machine instead of the substrate, on which line sensors 111 are arranged in matrix. The line sensors 111 are consist of two parts which are oriented in two directions, i.e., the scanning direction and the direction perpendicular thereto. When a calibration pattern light is projected from a projection optical system (not shown) to the line sensors 111 of the jig, the drawing start timing, positional deviation of the exposing light or the scanning region, and an inclination of the scanning region are detected for adjusting the exposure machine.
In addition, according to the method illustrated in FIG. 17, when the adjustment of the maskless exposure machine is finished, a film of aluminum, chrome or the like is formed on the principal surface of the substrate, and a photosensitive resist is further applied thereon. A reference pattern 106 is exposed on the substrate (see Stage (A) of FIG. 17), and a developing process, an etching process and a resist removing process are further performed so that a calibrating substrate is made. The photosensitive resist is applied on the substrate, and the substrate is led into the maskless exposure machine regularly so that the adjusted state of the apparatus is checked. Positioning the led substrate with the alignment marks disposed on the periphery thereof, hole patterns 108 piercing the resist are formed so as to have the same coordinates as the reference patterns 106 as their centers (see Stage (B) of FIG. 17). After the exposure process, a difference between the center position of the hole pattern 108 and the center position of the reference pattern 106 is measured as a positional deviation of exposure, and the adjustment is performed so as to eliminate the positional deviation (see Stage (C) of FIG. 17).
The maskless exposure machine that exposes a pattern on a resist film by scanning the resist film with a plurality of drawing heads emitting controlled light has no mask to be a criterion of dimensions, and hence it is required to perform calibration of the dimension of the drawing itself as well as check and calibration of functions of the exposure machine regularly so as to insure the accuracy. The items that require the accuracy insurance include rectilinearity, feed pitch accuracy, speed uniformity, drawing start timing and the like that are related to the stage for scanning operation, and include an inclination of the drawing head with respect to the scanning direction and a distance between the drawing heads when a plurality of drawing heads are used, which are related to optical characteristics. When these items are configured appropriately, the alignment accuracy with respect to the pattern of the base layer is improved.
The method of using the calibrating plate 110 illustrated in FIG. 16 is developed for a printed circuit board as a target. If a liquid crystal display (LCD) or an organic EL display (OLED) is a target, a fine wiring pattern is used as the exposure pattern. In this case, the line sensors 111 having high resolution for detecting the deviation of the exposure pattern must be developed, and high accuracy of positioning of the line sensor with respect to the calibrating plate is also required. It is difficult to satisfy these necessary conditions. In addition, it is a problem on a manufacturing site that the production must be stopped every time the calibration is performed. In addition, the method of using a test pattern substrate for the calibration illustrated in FIG. 17 requires to exposure the test pattern by another exposure machine that has finished the calibration during the development of the apparatus. Therefore, a problem with supply of the substrate may occur when a dimensions of the substrate is increased or in other cases. In addition, a problem may occur also about storage of the test substrate. In addition, a small variation of the exposure position surely exists even if the calibration is completed. Therefore, when the calibration is performed with respect thereto, the alignment error is added when the second exposure is performed. Therefore, there is a limitation in the accuracy control. Further, this case also has a problem that it is necessary to stop the production every time the calibration is performed on the manufacturing site.
In order to dispose the exposure pattern at the accurate position, it is necessary to perform a yawing correction of the stage on which the substrate is disposed to be moved when the scanning exposure is performed, and to maintain an arrangement of the projection optical system as a designed value for the scanning exposure. In general, a state of deviation of the pattern in a particular part of the exposed substrate is measured so that the exposure start timing and the arrangement of the projection optical system are adjusted. However, if the inclination of the stage is deviated, a deviation between scanning regions may occur due to the coordinates of the scanning region in a first direction even if the alignment state of the projection optical system is normal. Therefore, it is difficult to decide the arrangement state of the projection optical system from the deviation of the exposure pattern. As a result, the adjustment may be mistaken. It is considered that a part causing the deviation of inclination of the stage may be a length measuring system that is used for controlling the stage. Usually, the exposure machine has a laser length measuring machine for measuring a position of the stage ora yawing angle (inclination) When the inclination of the stage is measured by the laser length measuring machine, a plane mirror is attached to an end face of the stage, and two laser length measuring machines are disposed with a predetermined distance therebetween so as to be opposed to the plane mirror. Each of the laser length measuring machines emits a laser beam, and the laser beam reflected by the plane mirror is detected by a detection unit in the laser length measuring machine. The detection units of the two laser length measuring machines make the emitted laser beam and the incident laser beam interfere with each other, and hence the detection unit can detect the inclination of the stage with high accuracy from a change in interference fringe due to a change in optical length. Usually, the inclination of the stage is corrected based on the above-mentioned detection result. Here, the plane mirror has a precisely flat surface. However, if dimensions of the stage are increased along with an increase in size of the substrates, a size of the plane mirror is also increased so that it becomes difficult to ensure the flatness thereof. In addition, some methods of fixing the plane mirror to the stage may cause a distortion of the plane mirror. Further, pitch feed of the stage is performed also in a second direction so that the position where the laser beam enters the plane mirror is changed, and hence the inclination may be detected in error even if the stage has no inclined state. When the scanning exposure is performed, the stage is controlled and held in a certain constant direction. Therefore, if the inclination of the stage caused by the reason described above is not detected correctly, the inclination of the stage is corrected by error. The miscorrection of the inclination cannot be confirmed by monitoring a change in interference fringe, and the miscorrection can be decided only by a result of exposing a measuring pattern on the substrate and measuring the same. As described above, in order to improve the position accuracy of the exposed pattern, it is necessary to analyze each of the inclination of the stage, the exposure start timing and the arrangement deviation of the projection optical system precisely so as to perform correction. Conventionally, the test pattern is exposed on the jig serving as the reference or the substrate provided with the pattern serving as the reference for detecting the deviation of a measuring point, and hence the exposure position of the pattern is corrected according thereto. However, if the adjustment including the inclination of the stage is not performed, the adjustment of the exposure start timing and the arrangement of the projection optical system becomes imperfect. As a result, sufficient position accuracy of the pattern cannot be obtained. In addition, the method of using the calibrating jig or the test pattern substrate has the problem that the production must be stopped every time the exposure accuracy of the apparatus is checked on the manufacturing site.